The application of electrodynamic tethers in space applications is presently limited by the lack of a suitable plasma contactor device. Previously, the NASA Tethered Satellite System used an electron gun to emit electrons back into the conductive ionospheric plasma at the negative pole of the electrodynamic tether. Hollow cathode plasma generators were used on the Plasma Motor-Generator (PMG) tether mission. However, both, the electron gun and the hollow cathode are sensitive to contamination, depend heavily on spacecraft conditioned electrical power, and are complex. In particular, the Hollow Cathode requires a high pressure vessel and the associated pluming to regulate and handle the gaseous expellant.
Consequently, a plasma device that does not rely heavily on spacecraft resources (mass and conditioned electrical power) is desired. Also, the plasma device should be insensitive to contamination and, therefore, not require special on-orbit pre-operation conditioning or stand-by power and is capable of emitting large, multi-amp currents. In order to create such a plasma device, it is a requirement to emit large currents while minimizing the use of electrical power and expellant mass. Additionally, the device should use the emission of large currents at low power without the use of contamination-sensitive, low work-function materials.